The author took aim at the Bill which will make a series of amendments to the Gender Recognition Act, which has been in place since 2004.
Should the legislation be passed, it will drop the need for those wishing to change gender to show medical and psychiatric reports.
It will also slash the time someone has to live in their new gender from two years to six months.
Miss Rowling, 56, criticised Social Justice Secretary Shona Robison, who spoke in Holyrood last week about the Bill – but she praised author and journalist Susan Dalgety for her ‘most searing, heartfelt and courageous response yet’ to Miss Robison’s ‘astounding claim’.
Miss Robison told MSPs there was no evidence that ‘predatory and abusive men have ever had to pretend to be anything else to carry out abusive and predatory behaviour’.
Miss Dalgety, who was sexually assaulted as a child, branded the statement ‘crass’.
Miss Rowling tweeted: ‘The law @NicolaSturgeon’s trying to pass in Scotland will harm the most vulnerable women in society: those seeking help after male violence/rape and incarcerated women.
‘Statistics show that imprisoned women are already far more likely to have been previously abused.’